1. Field of the Invention
The present disclosure relates to fuel supply apparatus for supplying fuel, and in particular to a fuel supply apparatus in which fuel pumped by a low pressure fuel pump is further pressurized to have a high pressure by a high pressure fuel pump before being supplied to a target.
2. Description of the Related Art
Fuel injection systems for an internal combustion engine developed in recent years include a so-called inner-cylinder fuel injection system that directly injects high pressure fuel into a high pressure cylinder.
In a fuel supply apparatus in the inner-cylinder fuel injection system, a low pressure fuel pump and a high pressure fuel pump are placed in series, fuel in a fuel tank is temporarily controlled to a low pressure side target pressure by a low pressure fuel pump, fuel having a low pressure is thereafter converted to a high pressure by a high pressure fuel pump placed at a position near an injector, and the high pressure fuel is then injected from the injector.
In the fuel supply apparatus of the related art, a feedback control is performed so as to obtain the high pressure side target pressure by the use of a high pressure side pressure sensor for the high pressure fuel pump, and a feedback control is performed so as to obtain the low pressure side target pressure by the use of a low pressure side pressure sensor for the low pressure fuel pump.
Thus, the fuel supply apparatus of the related art requires at least two pressure sensors. The incorporation of multiple pressure sensors in pipelines results in excess labor and monetary, prevention structures, construction restrictions the cost of a sensor abnormality detection program as well as the costs for the pressure sensors themselves.
For example, related art described in US Publication No. 2010/0012096 (also published as Japanese Laid-Open Patent Publication No. 2009-540205) discloses a fuel injection apparatus for an internal combustion engine which feeds fuel in a fuel tank to a low pressure region by a feed pump, feeds fuel of the low pressure region to a high pressure region by a high pressure pump, and injects fuel of the high pressure region from an injector. A dedicated low pressure sensor for detecting the pressure in the low pressure region is provided in the low pressure region, and a dedicated high pressure sensor for detecting the pressure in the high pressure region is provided in the high pressure region. Moreover, in the low pressure region, the feed pump is controlled based on the pressure detected by the dedicated low pressure sensor and the high pressure pump is controlled based on the pressure detected by the dedicated high pressure sensor.
Furthermore, for example, related art described in Japanese Laid-Open Patent Publication No. 2006-175905 discloses a pressure control apparatus for brake liquid of a vehicle which enables the reduction in cost of as well as the simplification of the apparatus by controlling the braking force based on the pressures detected by front wheel pressure sensors, a rotational speed of a pump motor, and a liquid pressure estimated from a supply current. Additionally, such a system does not require the use of a relatively expensive liquid pressure sensor for detecting a supply pressure of a liquid pressure source (a gear pump).
Furthermore, related art described in Japanese Laid-Open Patent Publication No. 2007-263090 discloses a fuel injection amount control apparatus for an internal combustion engine which estimates a discharge pressure of a fuel pump based on a predetermined fuel pump characteristic and a detected fuel pump rotational speed.
In the related art described in US Publication No. 2010/0012096, pressure sensors are provided in both low and high-pressure regions. In the related art described in Japanese Laid-Open Patent Publication No. 2006-175905, a liquid pressure sensor is not incorporated, however, front wheel pressure sensors are still necessary. Furthermore, in the related art described in Japanese Laid-Open Patent Publication No. 2007-263090, the discharge pressure of the fuel pump is estimated from a fuel pump characteristic and an actual fuel pump rotational speed, however, due to the fact that a fluctuation of the discharge pressure based on the load of the fuel pump is not taken into account (if the load differs, the pressure differs even in the rotational speed), there is a possibility that the estimated accuracy of the discharge pressure is decreased.
Therefore, there has been a need in the art for further improving fuel supply apparatuses.